This invention relates to a robot end effector for pressing flexible workpieces, e.g. of fabric, onto and moving such workpieces over, a flat working surface.
A known robot end effector is shown in WO 86/03948 and comprises a sandwich construction consisting of a backing sheet, a facing sheet for gripping the workpiece and a resilient intermediate layer for accommodating irregularities, such as seams or unequal multi-;lies of fabric parts in subassemblies and local imperfections in the working surface. The backing sheet is U-shaped and the resilient intermediate layer and facing sheet are similarly shaped. In addition the thickness of the intermediate layer is less than the width of the facing sheet which has a relatively large surface area. Although this known end effector performs adequately for its predetermined task, i.e. gripping a workpiece during an unfolding operation and moving the workpiece along a defined path, its relative bulk renders it unsuitable for performing movements at the highest speeds required for modern processing.
It may be considered desirable for a sandwich construction end effector to have its backing sheet, facing sheet and intermediate layer all of the same size as a workpiece to be manoeuvred. However, this may result in the end effector being too bulky and having too high an inertia for effective, speedy manoeuvering. Furthermore, such a "solid" construction will result in air disturbance as an end effector is moved down on to a workpiece which will cause the latter to be displaced prior to contact between the effector and workpiece if the speed of movement of the end effector is not to be reduced to a slow approach.
The weight of an end effector can be reduced by only contacting a workpiece around its periphery. This is achieved by employing peripheral strips of facing sheet. When employing only strips of facing sheet the form of the resilient intermediate layer is important. Ideally it should be easily compressed, e.g. made of a soft foam material. However such easily compressed material tends to undergo shearing movement as the end effector moves a workpiece over a work surface. To some extent this tendency of the intermediate layer to undergo shearing movement can be counteracted by increasing the width of the intermediate layer. Such a solution is shown in WO 86/03948 in which the width of each strip of intermediate layer is considerably greater than its thickness. However this increased width of the strip-form intermediate layer increases the bulk of the end effector.
The present invention seeks to provide an improved form of robot end effector having a sandwich construction.